I don't know about business class, but first class is very difficult. Lufthansa has restricted availability significantly, but that's not the real problem. The real problem is the US Airways often can't see availability even when AC, UA & NH all see LH availability.
While some on this board have claimed there is a technical problem, I feel we're going down the same road as United a few years ago with Starnet blocking. If US won't address the issue, I would avoid buying miles unless you have flights on hold already (or have been told by US that the flights are available). Who knows what they will block next?